1. Field of the Invention
The invention relates generally to thin-film sensing devices, and more particularly to a thin-film resistive element and methods for fabricating the same.
An arrangement formed from two thin-film measurement resisters is used for the construction of a so-called hot-film anemometer. One of the thin-film measurement resisters works as a resistance heating element, while the other works as a temperature sensor. These resisters are formed from a thin structured metal film which is applied to a substrate with poor thermal conductivity, i.e. one characterized by a low specific heat capacity. The substrate is often made of glass and, in many cases, ceramic material. The problems associated with the use of ceramics arise in that the surface quality of the ceramic must be such that metal films can be applied homogeneously in the range of one micrometer or less in the first place. Such surface conditions are often not provided. The metal film forming the actual resistance element is generally made of platinum. However, the metal film, once applied, must be treated or structured in a suitable manner. This after-treatment is effected by erosion, i.e. removal of material, and the film resistor must first be structured and then trimmed. It is known from DE-PS 38 43 746 to provide the metal film with a meandering structure. Depending on the way in which such resistor elements are used in hot-film anemometers, a resistance to the process medium to be measured must be achieved in addition to the electrical and thermal characteristic. For this purpose, oxide or nitride films are conventionally provided for passivation. As a rule, this is effected by chemical vapor deposition with plasma enhancement, as the case may be.
It is therefore an object of the present invention to provide a process for producing a thin-film measurement resistor and to provide a thin-film measurement resistor element which reacts more quickly to changes in temperature, which is simple and economical to manufacture.
It is a further object of the present invention to provide a resistor element having a cover layer which is extremely resistant to corrosion.